Author | Shu Xinya Hubei Institute of Fishery Sciences
The crayfish is a benthic reptile crustacean whose diet has historically been controversial, with early views suggesting that the crayfish were a "herbivorous animal" and later long recognized as an "omnivorous" crustacean.
Recently, some scholars in the world's freshwater crawfish science have put forward the view that crayfish is a "carnivorous animal", but the mainstream opinion still believes that crayfish is an "omnivorous animal" that likes to eat animal foods. In natural waters, 98% of the food composition of crayfish is plant-based substances (Table 1), China's freshwater aquaculture community has always had "how many shrimp, look at aquatic grasses" saying, which shows the importance of aquatic plants in the crayfish farming process.
■ Table 1. Feeding and utilization of aquatic plants by crayfish
Aquatic plants are broadly divided into phytoplankton, low aquatic plants and higher aquatic plants. Phytoplankton mainly refers to single-celled algae floating in the water such as diatom phylum and phylum green algae, and low-grade aquatic plants mainly refer to multicellular low-grade plants such as kelp, unicorn and other multicellular algae and plants in peri-cluster organisms, and higher aquatic plants mainly refer to aquatic plants with vascular bundles. Aquatic plants are producers of aquatic ecosystems that can be used not only as food for crayfish, but also as food for many other aquatic animals, and some of these small animals that live on aquatic plants are also the food for crayfish.
Phytoplankton usually refers to the phytoplanktonic species of phytoplankton, including cyanobacteria, green algae, diatom, golden algae, yellow algae, dinoflagellate, dinoflagellate, cryptoalgae and naked algae, and about 9,000 species of freshwater algae are known to live in China. Phytoplankton plays an important role in the farming process of crayfish, most of the algae are good bait for crayfish larvae, juvenile shrimp and adult shrimp, and are also good food for zooplankton, especially in the stage of crayfish larvae and juvenile shrimp, crayfish larvae and juvenile shrimp mainly rely on feeding on these phytoplankton and zooplankton to develop and grow. In addition, as a producer of aquatic ecosystems, phytoplankton can absorb excess nitrogen, phosphorus, potassium and harmful substances in water bodies such as carbon dioxide, ammonia nitrogen, nitrate, nitrite, hydrogen sulfide and other harmful substances in water bodies, and release oxygen, dissolved oxygen in water is mainly produced by phytoplankton, phytoplankton plays an important role in maintaining the good and stable quality of water bodies, so phytoplankton also plays a very important role in the breeding process of crayfish.
The lower aquatic plants in freshwater are currently not well understood, and they are mostly multicellular plants, such as some species of brown algae and red algae, often on rocks, soil and other plant surfaces.
Higher aquatic plants are divided into four categories: submerged plants, floating plants, floating plants and water plants, and the colloquial "how many shrimp, look at aquatic plants" mainly refers to these higher aquatic plants. "How many shrimp, look at the water weeds", not the more aquatic weeds, the better, is the quality of aquatic weeds to be good, the types of aquatic weeds to be more, the number of aquatic weeds to be controlled, aquatic weed planting time, growth methods to be scientific.
There are many types of submerged plants, almost all submerged plants can be used for the cultivation of crayfish, but there is a difference of "suitable" or "more suitable", submerged plants on the cultivation of crayfish is "more beneficial than harmful". At present, the submerged plants used in crayfish farming mainly include pineapple, eye vegetable, black algae, bitter grass, goldfish algae, foxtail algae, Yile algae, etc. (Figure 1).
Figure 1. Crayfish farming in China is a common submerged plant
Submerged plants prefer pineapple, and Elegae is not the best aquatic plant. Pineapple grass, also known as wheat yellow grass, May yellow, Ezo grass, has been distributed in most parts of China, the amount of resources is very rich. Why are sunken plants preferred? First, the pineapple is a cold-water grass that grows in winter and spring, and the growth period is very consistent with the growth period of crayfish.
In China's Yangtze River Basin, the pineapple began to sprout in November, the whole winter is growing, and winter is the period when the crayfish overwinter without feeding, the growth of the pineapple will not be destroyed, the pineapple grows for a winter until March just connects with the crayfish to eat. From mid-May to early June, the seeds of pineapple began to die, and this is also the end of the harvest of crayfish, and the growth period of pineapple is very consistent with the crayfish farming period and is easy to plant; second, the utilization rate of pineapple is high. The leaves of the pineapple are large, the stems are tender and white, and the whole plant can be eaten by crayfish, and the edible rate is high; the third is that the crayfish love to eat, grow fast after eating, and have strong disease resistance.
Pineapple is rich in astaxanthin, carotenoids, vitamins and other active substances, crayfish like to eat, in the artificial breeding of pineapple and other aquatic weeds at the same time, crayfish will first eat pineapple, from Table 1 can also see the crayfish love of pineapple (Table 1). Huazhong Agricultural University College of Animal Husbandry with pineapple powder as an ingredient for egg and duck feed, the result of egg duck mostly produce red heart duck eggs, the test results also prove that the pineapple contains more astaxanthin, astaxanthin, carotenoids, lutein, vitamins and other active substances; fourth, the pineapple is a perennial aquatic weed, rich in resources, easy to obtain, and will not deteriorate the water quality.
It is widely distributed in most parts of China, north to Heilongjiang, south to Guangdong and Guangxi, east to Shanghai, Zhejiang, west to Xinjiang are distributed, the material is easy to obtain. Planted in shrimp ponds or rice paddies, because crayfish like to feed, the growth of pineapple can not keep up with the rate of feeding, and after planting, it will not grow like Elek algae and concentrate on death, causing water quality deterioration. Elezae is a submerged plant imported from South America in China, with small leaves, rough stems, low edible rate, and crayfish do not like to eat, so it is called "undefeated".
Because crayfish do not like to eat Elegae, the growth rate of Elezae in the cultured water body of crayfish is greater than the rate of being ingested, which often causes crazy growth, and it is very easy to cause water quality deterioration during the death period. In China's crayfish farming industry has been affected by one-sided publicity, a lot of money to plant Elekella, the Internet is also full of information on the sale of Elekella grass species, and did not make good use of their own around the pineapple resources. Now, farmers have begun to recognize the good role of pineapple grass, and there is a lot of information on the Internet about the sale of pine grass seeds.
Submerged plants are recommended to plant 3 to 4 species, the first choice is pineapple, and then choose 2 to 3 species from the black algae, eye vegetables, bitter grass, goldfish algae, foxtail algae, and Yile algae, and the area of submerged plants should be controlled at 30% of the area of the ring ditch and 50% of the platform. Ponds should be controlled at 50% as well. The planting time and planting method of submerged plants are also very important, to be scientific treatment, poor treatment of submerged plants is not good growth or can not be used in time for crayfish, or even completely can not be planted.
Rice field farming crayfish, although aquatic weeds are not as important as ponds, but if you can plant good pineapple grass on the surface of the rice field, plant good pineapps and other aquatic grasses in the rice field ring ditch and platform, it is also very helpful for crayfish farming.
Many farmers are very entangled in the cultivation of submerged plants, and even think that submerged plants are not planted well, the dissolved oxygen of the water body is low, and the crayfish is not well raised, which is incomplete. The role of submerged plants in crayfish farming is threefold: concealment, food, and regulating water quality. Concealment is its main role, followed by food, and the role of regulating water quality is very small. In fact, about 50% of the dissolved oxygen in natural water bodies is generated by phytoplankton photosynthesis, and 30% is the effect of air such as "interface action", "rainwater entry", "wind and wave effect", "atmospheric partial pressure effect" and other effects to make the oxygen in the air enter the water body, and the oxygenation effect of submerged plants is only 10%.
Submerged plants release oxygen during photosynthesis during the day and consume oxygen by breathing at night, while crayfish are nocturnal crustaceans, and at night is the time when crayfish need a lot of oxygen. We did an experiment in 2012 to stock the pineapple grass ball or snakeskin bag floater in the pond where there is no water grass, the pine grass ball or snakeskin bag floater plays the role of concealment, and the pine grass ball also plays a food supplement role, and the results have achieved better crayfish farming results.
Floating leaf plants refer to a type of plant whose roots are rooted in the soil and whose leaves float on the surface of the water, such as water lilies, spinach, diamond horns, and mustard fruits. At present, the use of floating plants in China's crayfish farming is very small, and in fact, the cultivation of crayfish by floating leafy plants is also "mixed". Floating leaf plants also have a hidden effect on crayfish, crayfish mainly hide in the surface of the floating leaves, especially when the bottom of the water body is lacking oxygen, the crayfish climb to the floating leaf back of the floating leaf plant in the surface water body or even above to hide, and the crayfish in the hulling stage can not use the floating leaf plant to avoid predators, so the concealment effect of the floating leaf plant is not as good as the submerged plant.
The food function of floating plants and the role of regulating water quality are not as good as those of submerged plants, so China's crayfish farming community rarely uses floating plants in the breeding stage. We have used a lot of lettuce as a habitat for crayfish juvenile shrimp in the breeding stage, especially in the northeast region, the tropical floating plant water hyacinth has not or very little, and we have made great use of lettuce to achieve good results.
Floating plants refer to a type of plant that floats on the surface of the water as a whole and floats with the wind, such as duckweed, locust leaf, water hyacinth, large grass, etc. (Figure 2). The role of floating plants in crayfish farming is also concealment, food and regulation of water quality, the role of concealment is the main, such as the use of water hyacinth, large grass as a concealment of crayfish juvenile shrimp in the breeding season, and duckweed can be used as a concealment and food, crayfish hide on the back of duckweed, but also like to eat duckweed.
The role of floating plants in regulating water quality in the process of crayfish farming is more to regulate the water quality and temperature of water bodies, and the effect on water oxygenation is smaller, but the cultivation of floating plants on crayfish is still "more beneficial than harmful".
At present, the floating plants commonly used in crayfish farming in China are water hyacinth, large grasshopper and duckweed, and also often floating in clusters of water peanuts on the surface of rice paddy ditches and pond surfaces as substitutes for floating plants. Water peanuts, also known as hollow lotus grass and dry lotus grass, are a terrestrial plant. The water peanut grass mass floats on the water surface, fixed with a bamboo pole, the water peanut floats on the water surface, will not grow as crazy as on land, the long stems and vines crisscross the formation of countless spaces for the crayfish to hide in the shelling and habitat, especially when the crayfish is dehulled, the water peanut grass clumps hidden on the surface of the water layer are very suitable and meet the conditions of sufficient dissolved oxygen, moderate pressure, suitable temperature, and invincible.
Therefore, we say that the use of water hyacinth in the breeding stage of crayfish, and the use of water peanuts as a hidden substance in the breeding stage is very conducive to the breeding and breeding of crayfish. It should be noted that no matter what kind of floating plants are used, the floating plants should be fixed to avoid floating plants drifting with the wind under the action of wind and waves, which is not conducive to the hiding of crayfish. There are many ways to fix it, for water hyacinth, duckweed, etc., it can be fixed with thin bamboo poles or ropes, and tied into triangles, rectangles, polygons with thin bamboo poles, and even fired into circles to fix floating plants and increase ornamentality. For water peanuts, thin bamboo poles can be inserted into the soil from the middle of the water peanut grass balls from top to bottom, which can be fixed or fixed with ropes (Figure 3).
Water hyacinth
Big grass (water cabbage)
Duckweed
■ Figure 2. Common floating plants
Standing water plant refers to the roots and rhizomes of plants growing in the bottom mud under the water surface, stems and leaves protruding from the water surface of a type of plant, common water plants are reeds, grass, water chestnut, lotus root, cress, cigu, white, lotus, lotus, rice and so on. The cultivation of crayfish by water plants is "more harmful than beneficial", and water plants without economic value must be removed from the crayfish farming water body. There are three reasons for this: First, the water plants, the stems and leaves grow out of the water, too many water plants, will reduce the crayfish habitat and crawling area, will greatly reduce the production of crayfish. Crayfish farming production is related to the crawling area of crayfish, the larger the crawling area, the higher the yield, and the production of rice field crayfish farming is lower than that of pond culture. Second, the water bird is easy to hide in the water plant area, the water bird is the natural enemy of the crayfish, and the water bird will greatly affect the production of the crayfish. Third, the water quality conditions in the dense areas of water plants are poor because the plants grow out of the water, which seriously affects the effect of wind and waves, and the water quality of the water quality of the water plants is weak, which often leads to the growth of crayfish being blocked.
Water peanuts
Water peanuts float on the surface of the water with rope fixation
Water peanuts float on the surface of the water with a bamboo pole fixed
■ Figure 3. Water peanuts replace the use of floating plants in crayfish farming
There are many kinds of aquatic plants, both submerged plants and floating plants, compatibility, quantity control is good, different aquatic plant growth periods are different, there are many types, each period has a good growth, the crayfish farming is very beneficial. The total area of submerged plants is not more than 50%, the total area of floating plants does not exceed 30% of the surface of the water, and the seasonal death of aquatic plants in a certain period will be small in area and will not deteriorate the water quality.
In addition to paying attention to the quality, type and quantity of aquatic grass, we must also pay attention to the planting time, planting location and planting method, planting different aquatic weeds in different places and planting different aquatic weeds at different times.
Location: Paddy field surface, platform, ring ditch bottom and ring ditch water surface, the key planting area of the paddy field is the rice field surface planting pineapple, paddy field shallow water platform planting pineapple, rotunda black algae, goldfish algae, ring ditch bottom planting pineapple, bitter grass, Yile algae, rice field ring ditch water surface breeding stage transplanted water peanut grass mass, transplantation of water hyacinth during breeding. The pond is mainly planted on the slope of the pond wall, silver leaf black algae, goldfish algae, bitter grass, Yile algae, and transplanted water peanut grass and water hyacinth on the surface of the pond.
Time and method: Aquatic plants can be planted or transplanted all year round, and different grasses are different at different times. For example, pineapple planted in October-March, sown in October, transplanted or cut in November-March; planted in 2-9 months, sown spores in 2-3 months, transplanted or cut in April-September; planted all year round; goldfish algae planted in 3 to 10 months, transplanted or cuttings; eleidella planted in 9-11 or 3-5 months, generally using cuttings; water hyacinth transplantation in 6-9 months, winter can be used to protect seeds; water peanuts can be transplanted all year round, transplanted leafless stem vines in winter, to be germinated in spring, spring, summer, Transplanted with leafy stem vines in the autumn. Transplant the water peanut grass balls on the surface of the water, with a gap of 4 meters in a clump, and the planting area does not exceed 30% of the area of the rice field ring ditch and 20% of the water surface of the pond.
Aquatic grass is planted "well", there are many hidden substances, food supplements, good water quality, and shrimp survival rate is high, growing large, and yielding high. If the aquatic weeds are not planted well and do not have to be entangled, you can use the method of releasing aquatic grass clumps or dropping broken mesh pieces, snakeskin bags and adding other concealments to make up for the loss of aquatic weeds that are not planted well.